seriously, if its taking that long, something is wrong. even on dial up i could have gotten that update overnight.
if you dont wish to redownload everything, a possible solution would be to use steams tool to check your files. if that doesnt work, try backing up your game, then deleteing the original files, then restoring the game.
also, post your system specs. it might be your PC or what else you do with it at the time. if your doing other things while its updating, that could fragment the files. or say if your computer has half a gig of ram or something like that, thats a horrible bottleneck just waiting for you to run 2 things at once so it can screw stuff up.